1. Field of the Invention
The present invention relates to an ink jet head used in an ink jet printer.
2. Description of Prior Art
Japanese Patent Laid-Open Publication No. H9-234864 discloses an example of an ink jet head. This ink jet head has a plurality of pressure chambers to which ink is supplied. The pressure chambers have one faces made of a common diaphragm. Provision is made such that a piezoelectric element bents the diaphragm to reduce the corresponding pressure chamber in volume, causing the nozzle connected to this pressure chamber to discharge the ink. Put on the common diaphragm is a common reinforcing plate, on which the piezoelectric elements are placed. Each individual electrode (upper electrode) is formed on the obverse surface of each piezoelectric element, while a common electrode (lower electrode) is formed on the reverse surfaces of the piezoelectric elements.
Each of the pressure chambers has a slender rectangular section in a plan elevation. In this ink jet head, such slender rectangular pressure chambers are transversely arranged. In this ink jet head, a block forming the pressure chambers is connected to a block forming an ink reservoir and ink discharge nozzles.
In this ink jet head of prior art, when it is intended to increase each maximum ink discharge amount such that the ink discharge can be controlled with good gradation, this introduces the problems that each pressure chamber is accordingly increased in size, a high dot density cannot be achieved and the entire head is increased in size. It is to increase the dot density as high as possible that each pressure chambers is formed in a slender rectangular shape. When each pressure chamber is formed in a slender rectangular shape, however, there is required high positioning precision for connecting the block forming the pressure chambers, the block forming the ink passages and the block forming the ink discharge nozzles to one another. This results in lowered yield.
It is an object of the present invention to provide an ink jet head which is advantageous in ink discharge control with good gradation, high dot density and compact head design.
The present invention achieves this object by improving an ink jet head in various points such as the diaphragm thickness, the deformation amount, the diaphragm shape (the shape of each of the openings of pressure chambers covered by the diaphragm), the arrangement of the pressure chambers and the like.
In an ink jet head comprising: a head main body in which formed are a plurality of pressure-chamber concave portions having supply ports for supplying ink and discharge ports for discharging ink; and a plate-like actuator which covers the pressure-chamber concave portions of the head main body, which forms a plurality of pressure chambers together with the pressure-chamber concave portions, and portions covering the pressure-chamber concave portions of which is deformable by field induction distortion serving as a drive source, causing ink in at least one pressure chamber to be discharged,
the ink jet head of the present invention is characterized in that the deformation amount of each deformable portion of the actuator is set such that the ratio A/V between the maximum discharge amount V (p1) of each pressure chamber and that area A (xcexcm2) of each deformable portion of the actuator which corresponds to the opening area of each pressure-chamber concave portion, is not greater than 10000.
The maximum discharge amount V refers to the maximum amount of ink to be discharged from each pressure chamber when each deformable portion of the actuator is bent and deformed one time toward the inside of each pressure chamber.
The ratio A/Vxe2x89xa610000 means that a large amount of ink can be discharged even though each deformable portion of the actuator is small in area. This is advantageous in ink discharge control with good gradation. Further, the smaller area of each deformable portion is more advantageous in both high dot density and compact head design.
Preferably, the ratio A/V is in the range of 6000 to 10000.
To obtain a deformation amount such that the ratio A/V is not greater than 10000, it is preferable that each deformable portion of the actuator has a thickness of not greater than 8 xcexcm and is made in the form of an oval in which the ratio L/S of the shorter diameter S to the larger diameter L is in the range of 1 to 3. According to such an arrangement, a large deformation amount can be obtained even though each deformable portion of the actuator is reduced in area. This is more advantageous in ink discharge control with good gradation, high dot density and compact head design.
Preferably, each deformable portion of the actuator has a maximum thickness in the range of 2 to 8 xcexcm.
Preferably, the actuator comprises: a diaphragm which covers the pressure-chamber concave portions of the head main body and which forms the pressure chambers together with the pressure-chamber concave portions; piezoelectric elements, each in the form of a thin film, respectively disposed for the pressure chambers and bonded to the diaphragm at the deformable portions thereof which form the pressure chambers, each piezoelectric elements being arranged to deform each deformable portion to discharge ink in each pressure chamber; and individual electrodes respectively disposed for the piezoelectric elements for applying a voltage thereto, each deformable portion of the diaphragm having a thickness of 1 to 5 xcexcm.
A field induction distortion of a piezoelectric element bends and deforms that deformable portion of the diaphragm to which this piezoelectric element is bonded. This changes the corresponding pressure chamber in volume to cause ink therein to be discharged. Since each deformable portion of the diaphragm has a thickness of 1xcx9c5 xcexcm, each deformable portion can be bent and deformed in a large amount as compared with its area.
In a ink jet head in which the pressure chambers are arranged in not less than three columns,
it is preferable that a group of electric contacts for individual electrodes, of the actuator, respectively disposed for the pressure chambers, is disposed outside of the outermost pressure-chamber column out of the pressure-chamber columns, and that a plurality of conductors for connecting, to the corresponding contacts of the group of electric contacts, the individual electrodes for the pressure chambers in the columns inside of the outermost pressure-chamber column, pass between adjacent pressure chambers in the outermost pressure-chamber column, the conductors above-mentioned passing at the head surface side.
More specifically, when the pressure chambers are arranged in not less than three columns, the dot density can be increased. However, if the electric contacts of the individual electrodes are disposed in the vicinity of the pressure chambers, it is required to provide contact spaces around the pressure chambers. This prevents the pressure chambers from being densely arranged. As a result, a number of ink discharge holes are extensively dispersedly disposed, contributing to the increase of the ink jet head in size. Thus, according to the present invention, there are utilized, as the wiring spaces, the spaces opposite to the top end faces of partition walls which partition adjacent pressure chambers (the spaces at the head surface side). Accordingly, the electric contacts can be gathered outside of the outermost pressure-chamber column, thus facilitating the wiring of the electric contacts. Further, the pressure chambers can densely be disposed. This is advantageous in both high dot density and compact head design.
When the ink jet head is arranged such that the plurality of pressure chambers are arranged in a plurality of columns, and that the actuator comprises: a diaphragm which covers the pressure-chamber concave portions of the head main body and which forms the pressure chambers together with the pressure-chamber concave portions; piezoelectric elements, each in the form of a thin film, respectively disposed for the pressure chambers and bonded to the diaphragm at the deformable portions thereof which form the pressure chambers, each piezoelectric elements being arranged to deform each deformable portion to discharge ink in each pressure chamber; and individual electrodes respectively disposed for the piezoelectric elements for applying a voltage thereto,
it is preferable that the piezoelectric elements and the individual electrode are formed, as overlapped each other in the same pattern, on the surface of the diaphragm, thereby to form drive portions and conductor portions,
the drive portions being formed, at the deformable portions, for deforming the same,
the conductor portions extending from the drive portions to the outside of the outermost pressure-chamber column out of the plurality of pressure-chamber columns, and
the conductor portions which extend from the drive portions of the pressure chambers in the columns inside of the outermost pressure-chamber column, passing between adjacent pressure chambers in the outermost pressure-chamber column, these conductor portions passing at the head surface side.
More specifically, when those portions of the partition walls between adjacent pressure chambers which are opposite to the head surface side, are utilized as the wiring spaces, it can be considered to dispose, at these spaces, conductors through insulation layers and to overlappingly connect the conductors onto the piezoelectric elements in the pressure chambers. According to such an arrangement, however, differences in level are produced at such connection parts, readily contributing to disconnection. Such a phenomenon of disconnection is remarkable particularly when thin-film conductors are used. Further, such connection is generally difficult.
According to the present invention, the piezoelectric elements and the individual electrode are formed, as overlapped each other in the same pattern, on the surface of the diaphragm thereby to form the drive portions and the conductor portions, and the conductor portions which extend from the drive portions of the pressure chambers in the columns inside of the outermost pressure-chamber column, pass between adjacent pressure chambers in the outermost pressure-chamber column. This does not produce the differences in level above-mentioned, and is therefore advantageous in the avoidance of disconnection. Further, as to the pattern formation, there is adopted a method of simultaneously patterning a laminated body of material films for piezoelectric elements and individual electrodes. This is also advantageous in production.
In an ink jet head comprising: a head main body in which formed are a plurality of pressure-chamber concave portions having supply ports for supplying ink and discharge ports for discharging ink; and a plate-like actuator which covers the pressure-chamber concave portions of the head main body, which forms a plurality of pressure chambers together with the pressure-chamber concave portions, and portions covering the pressure-chamber concave portions of which is deformable by field induction distortion serving as a drive source, causing ink in at least one pressure chamber to be discharged,
the ink jet head is preferably arranged to satisfy the three conditions that each of the deformable portions of the actuator which form the pressure chambers, has a thickness of not greater than 8 xcexcm, that the plurality of pressure chambers are arranged in a plurality of columns of which number is in the range 6 to 10, and that at the time when the ink jet head makes one scan in a main scanning direction, the dot density in an auxiliary scanning direction at a right angle to the main scanning direction, is not less than 300 dpi.
More specifically, even though it is intended to arrange pressure chambers as many as possible in a space having a predetermined length, there is still a limit in the number of pressure chambers which can be arranged, because it is required to assure the volumes of the pressure chambers. Accordingly, to achieve a dot density of not less than 300 dpi, the pressure chambers are required to be arranged in a plurality of columns. However, as the number of pressure-chamber columns is increased, the head itself is increased in size. Thus, when the number of the pressure-chamber columns is set in the range of 6 to 10 and the thickness of each deformable portion of the actuator is minimized, a high dot density of not less than 300 dpi can be achieved with no increase of the head in size.
More specifically, even though the opening area of each pressure-chamber concave portion (the area of each deformable portion) is small, a necessary discharge amount can be assured by minimizing the thickness of each deformable portion of the actuator. Further, the number of pressure chambers to be arranged in each column can be increased by reducing the area of each deformable portion. For example, when the dot density is increased from 300 dpi to 600 dpi, it is required according to a simple calculation to arrange, in each column, pressure chambers in twice the number. However, when the dot density is doubled, the discharge amount of ink to be discharged from each pressure chamber can be reduced to xc2xd or less, or xc2xc or less in certain cases, and the area of each deformable portion can therefore be reduced. Accordingly, the number of pressure chambers in each column can be increased and there is no need to excessively increase the number of pressure-chamber columns.
As to the three conditions above-mentioned, it is preferable that the actuator has a maximum thickness in the range of 2 to 8 xcexcm, that the number of pressure-chamber columns is in the range 6 to 10, and that the dot density is in the range of 300 to 1200 dpi.
In the ink jet head satisfying the three conditions above-mentioned, the actuator preferably comprises: a diaphragm which covers the pressure-chamber concave portions of the head main body and which forms the pressure chambers together with the pressure-chamber concave portions; piezoelectric elements, each in the form of a thin film, respectively disposed for the pressure chambers and bonded to the diaphragm at the deformable portions thereof which form the pressure chambers, each piezoelectric elements being arranged to deform each deformable portion to discharge ink in each pressure chamber; and individual electrodes respectively disposed for the piezoelectric elements for applying a voltage thereto, and each deformable portion of the diaphragm preferably has a thickness of 1 to 5 xcexcm.
Preferably, each deformable portion of the actuator is made in the form of an oval in which the ratio L/S of the shorter diameter to the larger diameter L, is in the range of 1 to 3.
More specifically, since each deformable portion of the actuator is in the form of an oval, a necessary ink discharge amount can be assured even though each deformable portion is small in area. Further, this is in advantageous in achievement of dot density of not less than 300 dpi with the column number of 6 to 10. Further, the fact that each deformable portion is made in the form of an oval in which the ratio L/S is in the range of 1 to 3, means that, even though the number of pressure-chamber columns is increased, the pressure chambers are not extensively dispersed in the main scanning direction. Accordingly, even though the nozzles (ink discharge ports) are formed immediately below the pressure chambers, the nozzle distances in the main scanning direction are not increased. This not only facilitates a signal processing for selectively discharging ink from nozzles, but also is advantageous in compact head design.
Preferably, the pressure chambers are arranged in zigzags such that the pressure chambers in each column are disposed at positions corresponding to the positions between the adjacent pressure chambers in each of adjacent column.
More specifically, the zigzag arrangement of pressure chambers enables the pressure chambers to be densely arranged and is therefore advantageous in compact head design.
In the ink jet head satisfying the three conditions above-mentioned, it is preferable that the ratio A/V between the maximum discharge amount V (p1) of each pressure chamber and that area A (xcexcm2) of each deformable port ion of the actuator which corresponds to the opening area of each pressure-chamber concave portion, is not greater than 10000.
More specifically, the ratio A/V of not greater than 10000 means that the ink discharge amount is large even though each deformable portion is small in area. This is advantageous not only in achievement of dot density of not less than 300 dpi with the column number of 6 to 10, but also in compact head design.
Preferably, the ratio A/V is in the range of 6000 to 10000.